The Decoupled Kinematics of High-z QSO Host Galaxies and Their Ly alpha Halos

We present a comparison of the interstellar medium traced by [C ii] (Atacama Large Millimeter/submillimeter Array), and ionized halo gas traced by Ly alpha (Multi Unit Spectroscopic Explorer), in and around QSO host galaxies at z similar to 6. To date, 18 QSOs at this redshift have been studied with both MUSE and high-resolution ALMA imaging; of these, 8 objects display a Ly alpha halo. Using data cubes matched in velocity resolution, we compare and contrast the spatial and kinematic information of the Ly alpha halos and the host galaxies' [C ii] (and dust-continuum) emission. We find that the Ly alpha halos extend typically 3-30 times beyond the interstellar medium of the host galaxies. The majority of the Ly alpha halos do not show ordered motion in their velocity fields, whereas most of the [C ii] velocity fields do. In those cases where a velocity gradient can be measured in Ly alpha, the kinematics do not align with those derived from the [C ii] emission. This implies that the Ly alpha emission is not tracing the outskirts of a large rotating disk, which is a simple extension of the central galaxy seen in [C ii] emission. It rather suggests that the kinematics of the halo gas are decoupled from those of the central galaxy. Given the scattering nature of Ly alpha, these results need to be confirmed with James Webb Space Telescope Integral Field Unit observations that can constrain the halo kinematics further using the nonresonant H alpha line.